eso9533 — Organisation Release

'Young Astronomers' Observe with ESO Telescopes

Educational Programme has Added Scientific Bonus

20 November 1995

Today, forty 16-18 year old students and their teachers are concluding a one-week, educational `working visit' to the ESO Headquarters in Garching (See ESO Press Release 14/95 of 8 November 1995). They are the winners of the Europe-wide contest `Europe Towards the Stars', organised by ESO with the support of the European Union, under the auspices of the Third European Week for Scientific and Technological Culture.

From November 14-20, they have worked with professional ESO astronomers in order to get insight into the methods and principles of modern astronomy and astrophysics, as carried out at one of the world's foremost international centres. This included very successful remote observations with the ESO 3.5-m New Technology Telescope (NTT) and the 1.4-m Coude Auxiliary Telescope (CAT) via a satellite link between the ESO Headquarters and the La Silla observatory in Chile, 12,000 kilometres away.

After a general introduction to modern astronomy on the first day of the visit, the participants divided into six teams, according to their interests. Some chose to observe distant galaxies, others prefered to have a closer look on binary stars, and one team decided to investigate a star which is thought to be surrounded by a proto-planetary system. Each team was supported by an experienced ESO astronomer. Then followed the observations at the remote consoles during three nights, the first at the NTT and the following at the CAT. Each team had access to the telescope during half a night. Although the work schedule - exactly as in `real' science - was quite hard, especially during the following data reduction and interpretative phase, all teams managed extremely well and in high spirits.

The young astronomers' observations were favoured by excellent atmospheric conditions. At the NTT, the seeing was better than 0.5 arcsecond during several hours, an exceptional value that allows very good images to be obtained. All observations represent solid and interesting science, and some of the new results are indeed at the frontline. Together with the team leaders, this will be followed up during the next months, with the likely result in the form of one or more scientific papers. It is difficult to think of an experience for young people that brings them closer to real science.

The stay at ESO is concluded today with the formal presentation of the team's reports, followed by a Press Conference. There will be a closing dinner this evening and tomorrow the participants will return to the respective countries and revert to normal life at the schools.

The entire event has been covered by assisting journalists and has also been documented by the ESO Video Team; a corresponding video film will become available shortly.

This experience has been very positive, both in terms of human relations, education and science. With their widely different cultural backgrounds and common interest in astronomy, the young people and their teachers have demonstrated the many virtues of international collaboration and thereby also made this event a valuable contribution to the integration of Europe.

The two Addenda to this Press Release contain information about the winning projects, and also, in a very provisional form, about the outcome of the work carried out at ESO.

More information

Addendum 1

The Projects of the National first-prize winners

Belgium:

This project aims at the theoretical description of a stable planetary system around another star and the possibilities to observe it from the Earth. A star of 0.8 solar mass is placed at the centre, surrounded with 3 terrestrial (Earth-like) planets and 4 planets of the gaseous, Jovian type. The distance from the Earth is 10 parsec, i.e. about 33 light-years. The project provides a very detailed description of these planets, their inner constitution, surface conditions and atmospheres. Many different observational approaches are described, but in the end it is appears that only infrared astrometry and astrometry would allow to detect the presence of the planets around this star.

Denmark:

This team performed extensive CCD-observations with the school telescope of three stellar clusters. The goal was to determine their HR-diagrammes (colour-magnitude) and other characteristics. Among others, the team succeeded to measure quite accurate B (blue) and V (green-yellow) colours of 40, 12-16-magnitude stars in the open stellar cluster NGC 6939. This allowed a determination of the distance (2500 parsec) to this cluster and its age (1800 million years), quite similar to the `professionally' determined values. As a side-result, and illustrating the faintness of starlight, a calculation showed that it would take no less than 437,236 years for the brightest star in the sky, Sirius, to heat a cup of coffee to the boiling point !

Finland:

This group used a 50-cm amateur telescope in their home town to observe the spectra of galaxies. A CCD spectrograph recorded the data which were then image-processed in the computer. For this programme, five galaxy pairs were selected and their velocities were measured. This allowed to calculate the distance to the galaxies by means of Hubble's law and also to determine the velocity difference between the two galaxies in a binary system. This in turn makes it possible to estimate the galaxies' total mass. When comparing these numbers with the mass of the visible objects, the group finally determined that the visible mass is only about 8 percent of the total mass, i.e. there must be much `dark matter' in these galaxies.

France:

This project concerned the actual construction of a working solar radio interferometer, a rather complex instrument that allows measurements of the long-wavelength radiation from the Sun and to map the locations in the solar corona where this radiation originates. The antennae and receiver were designed for frequences around 550 and 750 MHz and were built by the team members themselves. Radio signals from the Sun (as interference fringes) were effectively observed with this instrument, documenting the excellent functioning of this advanced equipment.

Germany:

Following a careful planning phase, systematic observations of the 14-magnitude planet Pluto were made with a CCD camera and a 30-cm telescope during 18 nights in the spring and summer of this year. Five nearby stars were used to calibrate the resulting photometric measurements. In the end, this programme was shown to achieve a very good photometric accuracy of about +- 0.2 magnitude per measurement. The variation of Pluto's brightness was found to be about 0.7 magnitude for this particular instrumental combination (no filtre). It was thus possible to draw the lightcurve which was found to be in complete agreement with the established 6.4 day rotation period.

Greece:

The project starts out from a star of 1.56 solar mass and a certain density. From this, its size, luminosity, temperature, pressure and other parameters are calculated. With an analogue to the Titius-Bode law for planetary distances, a new planetary system is constructed. It has 5 planets, 3 of which are of the terrestrial type and the other 2 are giant gas planets, larger than Jupiter. Their physical characteristics are calculated. One planet (the 3rd from the central star) is somewhat similar to the Earth, but it is too cold for life as we know it, and because of its comparatively small size, the atmospheric pressure is very low. It would in principle be possible to detect the outermost planet with the HST, if the distance to this planetary system was less than about 30 light-years.

Ireland:

The nearest star, Alpha Centauri, is a double star and a hypothetical planetary system around the A-component, a solar-type star, is studied in some detail. The presence of the companion star makes some planetary orbits unstable. In this project, 4 planets are placed within 2 AU (300 million km) of the central star; 3 of these are terrestrial (no. 3 is Earth-like) and the outermost is a small gaseous planet. Cometary orbits may be very complex in this gravitatinal field. A planetary system like the one described may be barely observable with the Hubble Space Telescope, and only if one of the planets passes in front of the star (an `occultation') and its light diminishes accordingly.

Italy:

This group built a spectrograph from scratch, with a grating and all the usual optical parts. They were able to calibrate the solar spectrum with the help of standard lamps and in this way, they observed several prominent, solar absorption lines. Among them were the H-alpha line at 6562 A, the sodium D-lines at 5890--96 And the magnesium triplet near 5175 A. These observations were made with the eye and also with the photographic recording technique. They were planning to observe the spectra of some stars also, but in the end time was too short and they had to hurry to send in the report.

The Netherlands:

This team has designed their own planetary system (with the name `Ngnz'i'!), consisting of a central star that is somewhat larger than the Sun and situated at the same distance as the Sun from the centre of the Milky Way System (31,700 light-years). The distance from the Sun is twice as large, 63,400 light-years. Circling the central star at a distance of 300 million kilometres, there is a double planet with a revolution period of just over 3 years. The conditions on another planet further out is suitable for life and it harbours frog-like intelligent beings. Two outer, gaseous planets complete this system.

Spain:

The group built its own f/8 Newtonian reflector with a main mirror of 20 cm diameter. They tested it on various astronomical objects and found that it produced quite good images. Then they put together their own CCD camera from spare parts; the frame size is about 5 x 4 mm with a total of 300,000 pixels. With this special equipment, they have observed the major Jovian moons as they revolve around Jupiter. They projected the image on a TV-screen and measured the exact positions of the moons, relative to Jupiter, on this screen. In this way, they were able to determine the periods of revolution of the moons and from the diameters of the orbits and Jupiter's size, they could determine Jupiter's mass and mean density.

Sweden:

In another Universe, three heroes meet on a far-away planet, named Magrathea. They check the computerized data archive available there, discovering a reference to the planetary system Ikaros III, and a description of its formation and evolution. At the centre is an A-type star, Ikaros; the temperature is 9700 K, and its lifetime is about 500 million years. It is surrounded by three planets, whose physical characteristics are listed in great detail. Two are small and dense and the outermost is gaseous. It turns out that the distance to our Earth is 26 light-years and that it would be not be too easy to observe the Ikaros system from here. It is unlikely that life can develop in this planetary system during the relatively short lifetime of the central star.

United Kingdom:

This project is directed towards variable stars of the pulsating type. It discusses the theory for these pulsations and the peculiar location of these types of stars in the HR-diagramme, as well as the technique to determine distances by means of measurements of the period. Once the period has been found observationally, the Period-Luminosity diagram makes is possible to find the luminosity and hence the distance to the star. The project also involved real measurements of an RR Lyr-type variable with a period of about 1/3 day. For this, a phototransitor and a registering device were used. The expected light variations were clearly seen.

Addendum 2

A brief summary of the results obtained at ESO

This brief description is based on the provisional data reduction and subsequent interpretation by the six teams, as presented during a final session on November 20, 1995. Further work will allow to quantify the results in greater detail. Each team was guided by a young ESO astronomer as Team Leader and was also provided support during the observations by ESO-astronomers Lex Kaper and Marcus Kissler, as well as by night assistants Vicente Reyes and Jesus Rodriguez (Garching), Hernan Nunez, Jorge Miranda and Victor Merino at (La Silla). For the data reduction, the teams used the MIDAS image processing system; the introduction was provided by Rein Warmels, one of ESO's experts on these matters.

Since the teams that were observing during the last night (3A and 3B) had very little time to reduce and interpret their data, it was not possible to carry these investigations to the same level of completeness as the others.

Team 1a:

This team used the multi-mode EMMI instrument at the 3.5-m NTT to observe so called `Interacting Galaxies'. These are galaxies which are so close to each other that their shapes are distorted by the action of their gravitational fields. Some of them are actually in a state of collision.

Direct CCD images were obtained of a total of 8 galaxies; 7 of these were observed in one colour (red) and 1 in two (red and yellow-green). The programme comprises a selection of different types of galaxies (Elliptical + Elliptical; Elliptical + Spiral; etc.) and different types of interactions (direct collision; fly-by; etc.). The observing conditions were quite good, with seeing from 0.5--1.2 arcseconds and some of the images obtained are probably the best ever made of these particular objects.

The team classified the types of involved, heavily distorted galaxies and attempted to decide what type of interaction is occurring. A very nice and instructive pictorial Atlas will be produced from this material.

Examples of Results from `Young Astronomers' Observations at ESOHere are just a few, very preliminary examples of the outcome of the observations performed by the 'Young Astronomers' during their visit to ESO on November 14 - 20, 1995. This file will be updated, as more images, etc. become available.

More details will be found in ESO Press Release eso9533.

Team 1b:

This team obtained short-exposure direct images and long-exposure long-slit spectra with NTT + EMMI of two peculiar galaxies, the edge-on distorted spiral NGC 1448 and the elliptical NGC 1947 which has a crossing dust lane. One IRAS superluminous galaxy was also observed. The latter part of the night was characterized by exceptionally good seeing (down to 0.3 arcsecond!), permitting to see many details in these galaxies, which have never been perceived before. For instance, several hitherto unknown dust lanes were found in the outer regions of NGC 1947 !

The slits were placed through the central part of the galaxies and along the major axis (NGC 1448) and the dust lane (NGC 1947), respectively. Strong emission lines of H-alpha, ionized nitrogen [N II] and ionized sulphur [S II] were seen in both galaxies; they originate in interstellar gas clouds within their confines.

From the exact wavelengths of these lines, the velocity of the galaxies can be measured. The team found values near 1100-1200 km/sec for both galaxies, in full agreement with the published values. Moreover, the variations of these line wavelengths at increasing distance from the galaxy centres allow to determine the rotation curves with good accuracy. A total amplitude of about 400 km/sec was observed in both galaxies. The velocity gradient is very steep at the centre, indicating the presence of a large mass in this area. Indeed, total masses of the order of 10e9 or even 10e10 solar masses were calculated for the innermost region of the galaxies.

Team 2a:

This team obtained high-dispersion spectra (resolution about 80,000) with the Coude Echelle Spectrometer and the 1.4-m Coude Auxiliary Telescope (CAT) of 5 late-type gaint and supergiant stars. These stars have arrived at a late phase of their lives. The heaviest, i.e. the supergiants may soon become supernovae, while the less heavy, the giants, may develop into a White Dwarf via the intermediate Planetary Nebula stage. The team wanted to find out which of these stars would develop which way by classifying them.

The spectra covered two spectral regions, at the hydrogen H-alpha 6562 A line and at the ionized calcium Ca II 8542 A line.

The calcium line serves for spectral classification; the deeper and broader this line is, the higher is the luminosity of the star. Of the five stars, T Microscopis and nu Eridanis were found to have a rather weak and narrow Ca II line and are therefore giants; the others had higher luminosity, in particular Alpha Orionis. In astronomical terms, the latter may in fact soon reach the supernova phase. One unknown emission line was found in the spectrum of this star; it will be interesting to try to identify it later.

Team 2b:

The object of the CAT observations by this team was the famous 4th-magnitude star Beta Pictoris which is known to have a surrounding disk of dust and gas. Recent observations indicate that planets may be forming in this disk at the present moment. Comparatively rapid changes in some spectral lines have been reported; the origin is unknown but may be infalling matter (comets?) on the star. The team decided to take a closer look at this.

A total of 12 spectra (1 a 5 min and 11 a 15 min exposure) were obtained at very high spectral resolution and high signal-to-noise ratio (better than 200). They cover the spectral region that includes the Ca II 8542 A absorption line. This line has a very complex structure in Beta Pictoris. At the bottom of the line is seen the sharp dip that results from absorption in the part of the disk that is in front of the star. Two H2O-lines from the terrestrial atmosphere also fall within this line profile.

All spectra were carefully calibrated and compared. For this, a mean spectrum was derived, and each of the 11 spectra was then divided by this. Deviations from the mean spectrum were present, in particular just redward of the disk absorption, and they were definitively larger than the very low observational noise. They may very well represent infalling bodies, but this is difficult to say on the basis of a preliminary data reduction. It will clearly be most interesting to continue the study of these spectra.

Team 3a:

This team decided to study two planetary nebula by means of high-dispersion CAT spectra. In these objects, most of the light is emitted in a small number of emission lines and the accurate determination of the shape and wavelength of these lines will allow to measure various parameters of the nebulae. For instance, the internal motion os the gas can be derived.

The first nebula was the well-known NGC 7293. The first spectra obtained showed splitting of the [S II] line; the two line components correspond to emission from the gas in the front and rear side of the nebula. The difference is 13 km/sec. This is important supplementary information to the observed geometric expansion of this nebula. It supports the derived age of about 50,000 years. The distance is found to be about 120 parsec, close to the nominal value. The other object observed, NGC 1535, is even younger, only about 3,500 years.

It will take some time to exploit the full information available in these very detailed spectra.

Team 3b:

This team, which observed during the second half of the last night at the CAT, decided to look at spectroscopic binary stars. These stars are detectable as such by temporal changes in their spectra. For instance, the orbital motion of the two components causes changes in the measured radial velocity. Moreover, the different temperatures of the components are reflected in the combined spectrum and it may also be possible to detect gaseous streams from one star to the other.

Two spectra were obtained of the suspected W Ursa Majoris type binary star Gamma Doradus with an internval of about 3 hours. This type of binary star consists of two components which are almost in contact and the rotation periods are short. Nevertheless, no changes were seen at all, casting some doubt on this proposed classification.

Seven more spectra were obtained of 4 Beta Lyrae type binaries; four covered the region of H-alpha and three the He I 6678 A line.

After a preliminary reduction of the data, the binary nature of three of them could be confirmed because of the presence of double lines, but for one, PU Puppis, only a single line was seen. Clear signs of circumstellar streams were not detected in any of them.